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Nervous system Y1 Harry And Heloise (with thanks to Ryan Devlin and Ed Whittaker for some slides)Structure for today Points Covered 1. Functions of the nervous system 2. Anatomy 3. Electrically Excitable Cells 4. Disorders of the Nervous System MCQs Questions are welcome throughout! What are you guys most interested in learning about?Function of the Nervous System Responses (automatic and voluntary) Movement Thoughts & Perceptions MemesOverview of Anatomy CENTRAL NERVOUS SYSTEM ● Brain ● Brainstem ● Spinal Cord PERIPHERAL NERVOUS SYSTEM ● All nerves from the spinal cord roots to neuro-muscular junction > spinal nerves, cranial nerves and peripheral nerves > contains sensory & motor neuronsAfferent v Efferent Afferent ▶ Sensory ▶ Dorsal root Efferent ▶ Motor ▶ Ventral rootAutomatic Responses - Autonomic NS Rest and Digest! Fight or Flight!Neurotransmitters of the Autonomic NS Key:Cells of the Nervous System: Main Types: • Neurones I) Excitable cells – the messengers II) Carry an electrical charge and transmit electrical currents • Glial Cells: I) The supporting cast II) Many subspecialisations: Myelination, structural support, regulating cellular environmentTypes of Neurone I) Sensory (afferent) Neurones II) Motor (efferent) Neurones III) InterneuronesTypes of Glial Cell I) Schwann cells (peripheral myelination) II) Oligodendrocytes (central myelination) III) Astrocytes (Most numerous! regulate CSF and support neurones) IV) Microglia (CNS macrophages) CNS PNSElectrically excitable cells - NeuronesThe basis of electrical excitability • All electrical currents in cells are conducted by movement of ions • Main ions are: Na , K , Cl and Ca 2+ • The phospholipid bi-layer is impermeable to ions, so ions can only move across the cell membrane through: I) Ion Pumps II) Ion Channels • These pumps and channels create potential differences to enable current flowResting potential – Creating a conc. gradient ● Na+/K+ATPase (3 Na+ for 2 K+) • K+ leak channels This makes intracellular environment more These are open at rest and allow K+ to –ve. Hence -70mV resting potential of leak back into ECF, counterbalancing neruones the Na+/K+ATPase to maintain resting potential Action potentials - what are they? • The electrical signals that convey info through nervous system • Allow fast and efficient signalling • This can be disrupted in diseaseAction potential - Depolarisation ● Inputs such as touch or compression deform membrane and open Na+ channels -70mv → -40mv ● This is down Na+ gradient! ● -40mV threshold breached - voltage gated Na+ channels open ● Rapid ‘All or nothing’ depolarisation to +30mV -40mV thresholdAction Potential - Repolarisation and Refractory Period ● Na+ channels close after 1ms and K+ channels open ● K+ moves the opposite direction, out of the cell - down K+ gradient! ● This is called repolarisation ● K+ efflux hyperpolarises cell - during this period Na+ channels are refractory ● Refractory period prevents AP travelling backwards ● Membrane potential resets to -70mVSaltatory Conduction ● Fatty cells called schwann cells insulate sections of neuron ● Gaps known as nodes of Ranvier ● ‘Jumps’ between nodes ● Enables faster conduction ● Unmyelinated = 1-10 m/s ● Myelinated = 60-120 m/s ● https://www.youtube.com/watch?v=ikFU v-gdNLQ (8:17)How action potentials encode information ● All action potentials same strength due to ‘all or nothing’ depolarisation ● Strength of signal conveyed by frequencyNeurotransmission at the synapseNeuromuscular JunctionPutting it all togetherNervous System DisordersHyponatraemia - ‘na’ = Na+ ▶ Clinically very significant - ~25% of acute hospital admissions ▶ Symptoms ▶ Muscle cramps ▶ Weakness, fatigue ▶ Altered mental state ▶ Risk of brain oedema ▶ Causes ▶ Diuretics ▶ Renal Disease ▶ Liver cirrhosis ▶ Congestive heart failure ▶ Serum conc <135mmol/L (will be given normal range)Hypernatraemia ▶ Not as significant - ~1% acute hospital admissions ▶ Symptoms ▶ tremor ▶ seizures and twitching ▶ hyper-reflexia ▶ convulsions ▶ intense thirst ▶ Risk of brain shrinkage and bleeding ▶ Causes ▶ renal failure ▶ fever, diarrhoea, vomiting ▶ Serum sodium >145mmol/LHypokalaemia- ‘ka’ = K+ ▶ Most common electrolyte disorder ▶ symptoms ▶ mild ▶ muscle weakness ▶ fatigue ▶ constipation ▶ cardiac arrythmia ▶ severe ▶ muscle paralysis ▶ resp paralysis ▶ GI paralysis ▶ Main risk is potentially fatal arrythmia ▶ causes ▶ diuretics ▶ renal disesase ▶ liver cirrhosis ▶ malnutritionHyperkalaemia ▶ symptoms ▶ neuromuscular, cardiac and GI impairment ▶ VF ▶ Risk of cardiac arrest ▶ Causes ▶ decreased kidney functions ▶ drug interactionsAction Potential Disorders Demyelinating diseases ▶ damage to schwann cells/oligodendrocytes and loss of myelin ▶ often due to autoimmune reaction ▶ Multiple Sclerosis (MS) ▶ patches of inflammation in brain ▶ loss of myelin in CNS axons ▶ Charcot-Marie-Tooth (CMT) ▶ most common inherited ▶ peripheral nerve conduction ▶ legs then arms and hands ▶ Guillain Barré ▶ inflammatory attack on PNS myelin - often follows episode of inflammatory illness ▶ tingling, abnormal sensation, weakness ▶ paralysis and resp failureMultiple Sclerosis ▶ Common (1 in 1000), with peak onset at 25-35 years ▶ Disease of the Central Nervous System (CNS) with multiple episodes of demyelination occurring at different times in different parts of the CNS ▶ The area of demyelination (‘plaque’) disrupts the conduction of a nerve impulse (i.e. saltatory conduction is blocked) ▶ Optic nerves, brain stem and spinal cord are the most commonly affected sites ▶ Symptoms include spasticity, weakness, sensory, urinary frequency, visual, double/blurred visionMultiple Sclerosis ▶ Various patterns of progression over time: ▶ Relapsing-remitting (85%) – inflammatory process ▶ Progressive (15%) – neurodegenerative process ▶ Relapsing-remitting leading to secondary progressive ▶ No cure. Mx is aimed at symptom control/reducing frequency of relapses/progression of disability ▶ Steroids – accelerate recovery following a relapse ▶ Pain-modulating drugs ▶ Physio/occupational therapy ▶ Immunomodulators/disease-altering drugs e.g. –zumabs. Reduce relapses by up to 70% ▶ Introduction of these drugs caused some controversy: ~£15K /year for newer drugs (zumabs)Peripheral Neuropathies ▶ Diabetic neuropathy ▶ chronic glucose dysreg ▶ damage to axons in distal limbs ▶ ulcerations, infections and gangrene ▶ autonomic ▶ loss of sympathetic and parasympathetic nerves ▶ poor circulation, Gi tract motility and healing ▶ risk of gangreneNeuritis ▶ inflammation of cranial nerves ▶ nerves become compressed ▶ optic ▶ loss of vision ▶ over several hours ▶ causes ▶ lyme disease ▶ viral encephalitis ▶ meningitis ▶ vestibular ▶ acute ▶ loss of vestibular function ▶ loss of balance and control of movementBell’s Palsy ▶ weakness or paralysis of facial muscles ▶ usually temporary ▶ cause ▶ viral inflammation ▶ Also known as CN VII palsySynaptic transmission disorders Myasthenia gravis (MG) ▶ Autoimmune - loss of ACh receptors ▶ worsening muscle weakness and fatigue ▶ improves with rest ▶ symptoms ▶ difficulties breathing, talking, chewing, swallowing ▶ difficulties with walking, climbing stairs ▶ facial praralysis or weakness ▶ double vision, difficulty maintaining gazeMotor Neuron Disease ▶ Group of neurodegenerative conditions that cause nerves in brain & spine to lose function. Characterised by progressive motor symptoms with normal sensation. ▶ Several types ▶ Most common: Amyotrophic Lateral Sclerosis (ALS) ▶ Primary Lateral Sclerosis ▶ Progressive Bulbar Palsy ▶ Spinal Muscular Atrophy ▶ Symptoms - Muscle Weakness ▶ May affect any muscles - usually starts in arm/legs, mouth ▶ Muscle pain/cramp/twitches/wasting ▶ Slurred Speech ▶ Weakened Grip ▶ Difficulty swallowing ▶ Often leads to difficulty in breathing which leads to respiratory complications ▶ Treatment is mainly supportiveReflex disorders ▶ Hyporeflexia ▶ depressed or absent reflexes ▶ Causes ▶ lower motor neuron lesions ▶ loss of motor neurons ▶ denervation of muscles (injury or disease) ▶ thyroid deficiency ▶ Hyper-reflexia ▶ exaggerated reflexes, spasticity and rigidity ▶ Causes ▶ upper motor neuron lesions ▶ spinal trauma or trans-section ▶ brain haemorrhage ▶ drug misuseMCQs!!You don't bother to revise for your end of semester MCQ. You see the first question and you feel your heart beating faster and muscles tense in preparation to run away. What is the MOST likely explanation for this response? A. stimulation of your sympathetic nervous system via pre-ganglionic neurones releasing ACh which stimulates post-ganglionic neurones to release noradrenaline B. stimulation of your sympathetic nervous system via pre-ganglionic neurones releasing noradrenaline which stimulates post-ganglionic neurones to release ACh C. stimulation of your parasympathetic nervous system via pre-ganglionic neurones releasing ACh which stimulates post-ganglionic neurones to release noradrenaline D. stimulation of your parasympathetic nervous system via pre-ganglionic neurones releasing noradrenaline which stimulates post ganglionic neurones to release AChYou don't bother to revise for your end of semester MCQ. You see the first question and you feel your heart beating faster and muscles tense in preparation to run away. What is the MOST likely explanation for this response? A. stimulation of your sympathetic nervous system via pre-ganglionic neurones releasing ACh which stimulates post-ganglionic neurones to release noradrenaline B. stimulation of your sympathetic nervous system via pre-ganglionic neurones releasing noradrenaline which stimulates post-ganglionic neurones to release ACh C. stimulation of your parasympathetic nervous system via pre-ganglionic neurones releasing ACh which stimulates post-ganglionic neurones to release noradrenaline D. stimulation of your parasympathetic nervous system via pre-ganglionic neurones releasing noradrenaline which stimulates post ganglionic neurones to release AChYou mistakenly enter Hive on a Tuesday, forgetting it is the infamous emo night. You begin to sweat and panic and start thinking "should I fight these mad goths or run away". Which of these is most likely to happen? A. Pupils constrict B. Bronchi constrict C. Peripheral vasoconstriction D. Decreased heart rateYou mistakenly enter Hive on a Tuesday, the bouncer looks straight at you and starts towards you. You begin to sweat and panic and start thinking "should I fight them or run away". Which of these is most likely to happen? A. Pupils constrict B. Bronchi constrict C. Peripheral vasoconstriction D. Decreased heart rateWhich disease below BEST FITS the following description?   A demyelinating CNS condition involving damage to oligodendrocyte cells, often due to an auto-immune reaction. Patches of inflammation in brain. A. Charcot Marie Tooth B. Multiple sclerosis C. Diabetic neuropathy D. Guillian Barre Syndrome E. Trigeminal neuralgiaWhich disease below BEST FITS the following description?   A demyelinating CNS condition involving damage to Schwann cells, often due to an auto-immune reaction. Patches of inflammation in brain. A. Charcot Marie Tooth B. Multiple sclerosis C. Diabetic neuropathy D. Guillian Barre Syndrome E. Trigeminal neuralgiaWhich of these are the most numerous cell type in the brain? A. Neurons B. Schwann Cells C. Ganglion Cell D. Astrocytes E. LeukocytesWhich of these are the most numerous cell type in the brain? A. Neurons B. Schwann Cells C. Ganglion Cell D. Astrocytes E. LeukocytesMyelination of a neurone causes: A. Slower conduction due to the added thickness making the diffusion distance greater B. Faster conduction as the nodes of ranvier don't need to depolarise C. Faster conduction as only the nodes of ranvier depolarise D. No overall difference in speed of conductionMyelination of a neurone causes: A. Slower conduction due to the added thickness making the diffusion distance greater B. Faster conduction as the nodes of ranvier don't need to depolarise C. Faster conduction as only the nodes of ranvier depolarise D. No overall difference in speed of conductionWhich of the following is an example of a disease affecting neurotransmission that attacks ACh receptors? A. Charcot-Marie-Tooth disease B. Myasthenia Gravis C. Multiple Sclerosis D. Guilian-Barre SyndromeWhich of the following is an example of an disease affecting neurotransmission that attacks ACh receptors? A. Charcot-Marie-Tooth disease B. Myasthenia Gravis C. Multiple Sclerosis D. Guilian-Barre SyndromeFeedback Please take a minute now before you leave to fill in a quick feedback form: https://app.medall.org/feedback/anonymous?organisation= accessibility-in-medicine&keyword=eeb5b57f7150be960a01a 4c3&fbclid=IwAR1jjUSsG0vu9HSjTPGbxya_Vhf9rlqMq3g27qMi DcKBMVk_6e_JzFRTUR0 AIM Facebook Page ▶ Give our Facebook page a like for updates and opportunities,just search @AIMEdinburgh▶ If you have any more questions, feel free to email us at s1609832@ed.ac.uk and s1711519@ed.ac.uk or email accessibilityinmedicine@gmail.com